You call forth an aberration, a horror from beyond mortal understanding.  As you read the bizarre and maddening text from the material components of this spell, your mind begins to bend and twist in order to draw the creature into being from your very imagination. Make a DC12 Intelligence saving throw. On a failure, you gain a form of long-term madness that lasts for the spell's duration. Regardless of the result of your saving throw, the creature in question appears in a space within range of the mirror you used to summon it. An aberration summoned this way has a maximum challenge rating of CR3.

If an aberration summoned by this spell has one or more major eyeball, the eyeballs you used to summon the creature is consumed. While you maintain concentration, you and any aberration summoned by this spell can communicate telepathically as long as you are on the same plane of existence. Aberrations summoned by this spell disappear when they drops to 0 hit points.

The aberration is friendly to you and your companions for the duration. Roll initiative for the aberration, which has its own turns. It obeys any verbal or telepathic commands that you issue to it (no action required by you). If you don't issue any commands to the aberration, it defends itself from hostile creatures but otherwise takes no actions.

If your concentration is broken, the aberrations don't disappear. Instead, they randomly gain a form of madness, and you lose control of them. If their madness or alignment dictates it, they become hostile to nearby creatures and might attack. An uncontrolled aberration can't be dismissed by you and it fades from existence 1d10 rounds after you lose control of it.

The GM has the aberrations statistics. Sample aberrations can be found below. 

At Higher Levels. When you cast this spell using a spell slot of 5th level the creature's maximum challenge rating becomes CR5. When you use a spell slot of 7th level or higher, the creature's maximum challenge rating becomes CR6. When cast with a 9th level spell slot, you can summon multiple creatures, up to four CR1s, three CR2s, or two CR3 or CR4. 

Sample Aberrations